Can Japan 3D Buildings be partially hidden in Unreal Engine?

sung.sung · June 17, 2024, 12:08am

I would like to hide some of the Japan 3D Buildings in Unreal Engine as shown in the link below.

please give me a brief step-by-step guide.

Kevin_Ring · June 17, 2024, 2:36am

The page you linked pretty much is the brief step-by-step guide. If you’re running into trouble somewhere specific, let us know where and maybe we can help.

sung.sung · June 17, 2024, 2:56am

Hi @Kevin_Ring ,

So you are sure that clipping is possible in Japan 3D Buildings as well as in World Terrain by doing the same thing as with Link?

janine · June 18, 2024, 1:33pm

Hi @sung.sung,

Yes, clipping is possible for the Japan 3D Buildings, as well as any other 3D Tilesets you want to use. You just have to follow the same instructions in the tutorial that Kevin linked. Let us know if you run into any issues!

sung.sung · June 21, 2024, 10:24am

Hi @janine ,

I placed the 3D model in the hall after clipping Cesium World Terrain.
When I played the game, the physics along the shape of the Cesium World Terrain caused the player to float in the air.
I would like to know how to disable physics only inside the clipping.

janine · June 25, 2024, 7:44pm

Hi @sung.sung,

Polygon clipping is more of a visual effect. It hides the meshes, but that doesn’t mean they completely disappear. In fact, the physics meshes may still exist, which will make it seem like the player is floating on air.

You can improve this behavior by using the Exclude Selected Tiles property on the CesiumPolygonRasterOverlay. Tiles that are completely clipped by the polygon (i.e., no part of them is visible) will not be rendered at all, so their meshes won’t exist in the level. However, tiles that are partially visible (because they’re on the edge of the polygon) will still have physic meshes created, so there may be partial intersections around the outskirts.

I should advise that we’re currently experiencing regressions in this functionality. We’re tracking these issues on Github here:

github.com/CesiumGS/cesium-native

Degenerate triangle test in pointInTriangle breaks CartographicPolygon

opened 07:18AM - 25 Jun 24 UTC

kring

bug

A 3D point-in-triangle test was added in #826, and at the same time a test for "…degenerate triangles" was added to the 2D point-in-triangle test: ```cpp // Return false for degenerate triangles. if (glm::length2(ab) < CesiumUtility::Math::Epsilon8 || glm::length2(bc) < CesiumUtility::Math::Epsilon8 || glm::length2(ca) < CesiumUtility::Math::Epsilon8) { return false; } ``` Unfortunately this breaks `rectangleIsWithinPolygons` and `rectangleIsOutsidePolygons` in `CartographicPolygon`, which in turn breaks the ability to filter out tiles that are entirely inside or entirely outside a clipping polygon. These functions operate in longitude/latitude space with units of radians. They form two triangles from the bounding rectangles of the polygon and the tile, and test various points against these triangles. But in longitude/latitude radians, these triangles are very small. The length squared of their edges is significantly less than 1e-8, and so this test flags them as degenerate even though they most definitely are not. By the way, this test won't even detect all the possible degenerate triangles. If I have three vertices arranged on a line but far apart from each other, that's a degenerate triangle but the test in this function won't detect it. I once told someone that epsilons are the root of all evil. That's a little extreme, but only a little. 😁 One thing we can say that is definitely less extreme, though, is that a function like this, which is inherently unitless, _must not_ have an absolute epsilon. If we knew we were working with meters, then we could maybe say "we don't care about triangles smaller than a nanometer, so we can ignore those." But if we don't know the units, we can't make any assertions like that. A relative epsilon could be ok. Testing the vertices for equality with a relative epsilon of 1e-14 or so would be unlikely to cause a false positive. But in my opinion, a function like this just shouldn't have a degenerate triangle test at all. Without one, the worst-case scenario is that you intermittently might detect an intersection with a triangle that is degenerate, or close to it. But you'd detect that intersection pretty much where the line or point pretending to be a triangle is actually located, so no one is likely to be surprised by that. Floating point fun could mean that a point that is not quite on the line mathematically gets flagged as being inside the "triangle", but that's no different or worse than when the same floating point fun deems a point very slightly outside a valid triangle to be inside it. On the other hand, if you add a degenerate triangle test, and it's a little too eager, you end up completely missing intersections that _actually exist_. That's a drastically worse situation, in my view.

We’re working to fix these ASAP, so stay tuned for updates.

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Can Japan 3D Buildings be partially hidden in Unreal Engine?

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